Non-rotating flexure bearings for cryocoolers and other devices

ABSTRACT

A system includes a device, a support structure, and a flexure bearing configured to connect the device to the support structure. The flexure bearing includes an outer hub and an inner hub, where the hubs are configured to be secured to the support structure and to the device. The flexure bearing also includes multiple sets of flexure arms connecting the outer and inner hubs. Each set of flexure arms includes symmetric flexure arms. The flexure bearing could include three sets of flexure arms positioned radially around a central axis of the flexure bearing and having a spacing of about 120°. Each flexure arm can follow a substantially curved path between the outer hub and the inner hub. The symmetric flexure arms in each set can be configured such that twisting of one flexure arm in one set is substantially counteracted by twisting of another flexure arm in that set.

TECHNICAL FIELD

This disclosure is directed to devices for holding components in desiredlocations. More specifically, this disclosure is directed tonon-rotating flexure bearings for cryocoolers and other devices.

BACKGROUND

Cryocoolers are often used to cool various components to extremely lowtemperatures. For example, cryocoolers can be used to cool focal planearrays in different types of imaging systems. It is often necessary ordesirable to secure certain components of a cryocooler in fixedpositions relative to other components of the cryocooler. This may beneeded, for example, to ensure proper operation of the cryocooler or toreduce disturbances in the cryocooler or in an overall system. Oneapproach to securing components of a cryocooler involves the use offlexure bearings that connect moving mechanisms of the cryocooler to asupport structure. A conventional flexure bearing includes arms arrangedin a spiral pattern, where the arms extend between a moving mechanism ofthe cryocooler and the support structure.

SUMMARY

This disclosure provides non-rotating flexure bearings for cryocoolersand other devices.

In a first embodiment, an apparatus includes an outer hub and an innerhub, where the hubs are configured to be secured to a support structureand to a device. The apparatus also includes multiple sets of flexurearms connecting the outer hub and the inner hub. Each set of flexurearms includes symmetric flexure arms.

In a second embodiment, a system includes a device, a support structure,and a flexure bearing configured to connect the device to the supportstructure. The flexure bearing includes an outer hub and an inner hub,where the hubs are configured to be secured to the support structure andto the device. The flexure bearing also includes multiple sets offlexure arms connecting the outer hub and the inner hub. Each set offlexure arms includes symmetric flexure arms.

In a third embodiment, a method includes displacing a device coupled toa flexure bearing. The flexure bearing includes an outer hub and aninner hub, where the hubs are configured to be secured to the device andto a support structure. The method also includes deforming flexure armsin the flexure bearing as a result of the displacement. The flexurebearing includes multiple sets of flexure arms connecting the outer huband the inner hub. Each set of flexure arms includes symmetric flexureanus. The method further includes substantially preventing rotation ofthe device during the displacement.

Other technical features may be readily apparent to one skilled in theart from the following figures, descriptions, and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of this disclosure and its features,reference is now made to the following description, taken in conjunctionwith the accompanying drawings, in which:

FIG. 1 illustrates an example system with non-rotating flexure bearingsaccording to this disclosure;

FIGS. 2 and 3 illustrate an example non-rotating flexure bearingaccording to this disclosure;

FIGS. 4 through 6 illustrate other example non-rotating flexure bearingsaccording to this disclosure; and

FIG. 7 illustrates an example method for using a non-rotating flexurebearing according to this disclosure.

DETAILED DESCRIPTION

FIGS. 1 through 7, described below, and the various embodiments used todescribe the principles of the present invention in this patent documentare by way of illustration only and should not be construed in any wayto limit the scope of the invention. Those skilled in the art willunderstand that the principles of the present invention may beimplemented in any type of suitably arranged system.

FIG. 1 illustrates an example system 100 with non-rotating flexurebearings according to this disclosure. As shown in FIG. 1, the system100 includes a compressor 102, which can be used with other components(not shown) to form a cryocooler. A cryocooler generally represents adevice that can cool other components to cryogenic temperatures or otherextremely low temperatures. In FIG. 1, the components on the left sideof FIG. 1 are mirrored on the right side of FIG. 1, and for convenienceonly the components on one side of the compressor 102 are identifiedusing reference numbers.

In this example, the compressor 102 includes a motor magnet 104 and amotor coil 106 that operate to cause movement of a compressor piston108. The piston 108 strokes back and forth during each compressioncycle, which causes repeated pressure changes in a fluid that isprovided through a transfer line 110. Controlled expansion andcontraction of the fluid creates a desired cooling of one or morecomponents. Note that this represents one specific implementation of acompressor 102 and that any other suitable compressor can be used in thesystem 100.

The compressor 102 and other components of a cryocooler (such as anexpander and balancer units) are positioned within a housing 112, whichis sealed by an end cap 114. The housing 112 represents a supportstructure to which the compressor 102 is mounted. The housing 112includes any suitable structure for encasing or otherwise protecting acryocooler (or portion thereof). The end cap 114 represents any suitablestructure for closing a cryocooler housing.

In order to help precisely control the positioning of the compressor102, multiple flexure bearings are provided to mount the compressor 102to the housing 112. In this example, there are multiple stacks 116 a-116b of flexure bearings. Each stack 116 a-116 b can include one ormultiple flexure bearings. As described in more detail below, eachflexure bearing generally includes an outer hub, an inner hub, andflexure arms. The outer and inner hubs can be secured to a supportstructure (such as the housing 112) and to a device that includes amovable component (such as the compressor 102 or other portion of acryocooler). The flexure arms couple the outer and inner hubs. Symmetricsets of flexure arms are configured to help prevent rotation of thedevice when the device is displaced. Example embodiments of the flexurebearings are described below.

As noted above, one conventional flexure bearing includes arms arrangedin a spiral pattern, where the arms extend between a moving component ofa cryocooler and a support structure. While this conventional flexurebearing can generally hold the moving component of the cryocooler at adesired location, one problem with this design is that it allows themoving component to rotate. Rotation of the moving component can causedisturbances in the operation of a larger system (referred to as“exported disturbances” of the cryocooler). The non-rotating flexurebearings described in this patent document help to both securecomponents of a cryocooler in place and reduce or eliminate rotation ofthe components. Among other things, this helps to reduce or minimizeoff-axis vibrations and moments of the components. Such off-axisvibrations and moments are inherent in spiral-designed flexure bearings.While the components of a cryocooler may still be disturbed in theirpositions, the use of the non-rotating flexure bearings can allowextremely low levels of exported disturbances from the cryocooler to beobtained. This can be useful, for instance, in helping to keep thecompressor pistons 108 aligned with their respective bores.

The cryocooler can be used to cool any suitable components. For example,the cryocooler could be used to cool a focal plane array, whichrepresents an image sensing device used in various types of applicationsincluding infrared sensors. However, the cryocooler could be used tocool any other suitable components of a system. Other example uses forthe cryocooler include cooling computing components (such asprocessors), radio frequency components in telecommunication and deepspace communication equipment (such as RF filters), components inmagnetic resonance imaging (MRI) systems, and superconductingelectronics. These uses are for illustration only, and the cryocoolercan be used to cool components in any other type of system.

Note that the compressor 102 in FIG. 1 represents a portion of acryocooler, and the cryocooler could include various other components,such as an expander and balancer units. The expander, balancer units, orother components of the cryocooler could also include moving components,and one or more non-rotating flexure bearings could be used with thosemoving components in the same or similar manner as that described above.

Although FIG. 1 illustrates one example of a system 100 withnon-rotating flexure bearings, various changes may be made to FIG. 1.For example, while described as coupling a compressor 102 to a housing112, one or more flexure bearings could be used to help secure any othersuitable components to any suitable support structure. The non-rotatingflexure bearings are not limited to use with cryocoolers.

FIGS. 2 and 3 illustrate an example non-rotating flexure bearing 200according to this disclosure. The flexure bearing 200 could be used inany suitable system. For example, the flexure bearing 200 couldrepresent the flexure bearings contained within the stacks 116 a-116 bin the system 100 of FIG. 1.

As shown in FIG. 2, the flexure bearing 200 includes an outer hub 202and an inner hub 204. The outer hub 202 can be secured to a supportstructure, and the inner hub 204 can be secured to a device (such as acompressor 102 or other component of a cryocooler). Alternatively, theouter hub 202 can be secured to a device, and the inner hub 204 can besecured to a support structure. The flexure bearing 200 thereby helps tosecure the cryocooler component or other device at a desired locationrelative to the support structure. While the device may be temporarilydisplaced due to external forces, the flexure bearing 200 helps toquickly return the device to the desired location. As shown in FIG. 1,multiple flexure bearings 200 can be used (such as in a stack) to helptune the spring stiffness and thus the natural frequency of the movingmechanism in the cryocooler or other device.

Note that the circular shapes of the hubs 202-204 are for illustrationonly. Each hub 202-204 of the flexure bearing 200 could have anysuitable size, shape, and dimensions. In particular embodiments, theouter hub 202 has an inner diameter of about 4.7 inches (about 119.38mm) and an outer diameter of about 5.4 inches (about 137.16 mm), and theinner hub 204 has an inner diameter of about 1.375 inches (about 34.925mm) and an outer diameter of about 2.42 inches (about 61.468 mm).

Each hub 202-204 includes various openings 206. The openings 206 arearranged to receive connectors for coupling the flexure bearing 200 tothe support structure and to the cryocooler component or other device.For example, each opening 206 could allow a bolt to be inserted througha hub 202-204 in order to secure the flexure bearing 200 to the supportstructure or to the cryocooler component or other device. Each opening206 could have any suitable size, shape, and dimensions. Note, however,that any other suitable mechanism could be used to secure the flexurebearing 200.

As shown in FIG. 2, the flexure bearing 200 also includes three sets 208a-208 c of flexure arms. The sets 208 a-208 c of flexure arms couple theouter hub 202 and the inner hub 204. As a result, when the flexurebearing 200 is secured to a support structure and to a cryocoolercomponent or other device, the sets 208 a-208 c of flexure arms help tohold the cryocooler component or other device at a desired location.Even though external forces can cause deformation of the flexure armsand movement of the cryocooler component or other device, the flexurearms operate to return the device to the desired location. In theexample shown in FIG. 2, there are three sets 208 a-208 c of flexurearms positioned radially around a central axis at a spacing of about120°.

Each flexure set 208 a-208 c includes two flexure arms 210 a-210 b. Theflexure arms 210 a-210 b in each set 208 a-208 c are mirror images ofone another, meaning the flexure arm 210 a in one set is a mirror imageof the flexure arm 210 b in that set. The flexure arms 210 a-210 b ineach set 208 a-208 c are therefore symmetric, meaning the load pathconnecting the hubs 202-204 is symmetric. As can be seen in FIG. 2, eachflexure arm 210 a-210 b is connected to the outer hub 202 and follows awinding path with various “S” curves to the inner hub 204. The pathfollowed by each flexure arm 210 a-210 b generally includes a “loopback” region 212 where the flexure arm 210 a-210 b substantiallyreverses direction within the flexure bearing 200. Note that while eachflexure arm 210 a-210 b is shown here as being curved along most or allof its path, this need not be the case.

In the following discussion of various flexure bearings, reference ismade to an “axial” direction. The “axial” direction refers to thedirection along a central axis of a flexure bearing, meaning along thecentral axis of the flexure bearing 200 that is perpendicular to theimage shown in FIG. 2. This is in contrast to a “radial” direction,which refers to the direction from the central axis of the flexurebearing 200 out towards the outer hub 202 in FIG. 2.

As noted above, the outer hub 202 of the flexure bearing 200 can becoupled to a support structure, and a cryocooler component or otherdevice can be coupled to the inner hub 204 of the flexure bearing 200.In this configuration, the flexure arms can flex and twist, but theinner hub 204 does not rotate significantly (or at all) when thecryocooler component or other device is displaced axially along thecentral axis of the flexure bearing 200. As shown in FIG. 3, this isbecause deformation of one flexure arm 210 a in a set 208 a-208 c isassociated with a substantially opposite deformation of the otherflexure arm 210 b in the same set 208 a-208 c. In other words, due tothe symmetry of the flexure arms 210 a-210 b in each set 208 a-208 c,the inner hub 204 does not rotate as a function of displacement. As aresult, the deformations of the flexure arms 210 a-210 b within each set208 a-208 c substantially cancel each other, resulting in little or norotation of the inner hub 204. Note that if the outer hub 202 of theflexure bearing 200 is coupled to a device and the inner hub 204 of theflexure bearing 200 is coupled to a support structure, the samemechanism can help to reduce or minimize rotation of the outer hub 202.

Moreover, the design of the flexure arms 210 a-210 b in each set 208a-208 c can be chosen so that the natural frequency of the flexurebearing 200 (with one hub 202-204 secured to a cryocooler component orother device) does not couple with the operating frequency of thecryocooler component or other device. For example, the natural frequencyof the flexure arms 210 a-210 b could be around 80 Hz to around 120 Hz.If used with a compressor 102 having an operating frequency of about 40Hz to about 60 Hz, the flexure arms 210 a-210 b are not be susceptibleto dynamic amplification (or are susceptible to an extremely smallextent).

The flexure bearing 200 could be formed from any suitable material(s).In some embodiments, the flexure bearing 200 can be formed fromstainless steel or flapper valve steel, such as BÖHLER-UDDEHOLM 716 UHBstainless steel. The flexure bearing 200 can also have any suitablesize, shape, and dimensions. As particular examples, the flexure bearing200 could have a thickness of about 0.008 inches (about 0.2032 mm),about 0.01 inches (about 0.254 mm), about 0.022 inches (about 0.5588mm), or about 0.0315 inches (about 0.8 mm). The flexure bearing 200 canfurther be formed in any suitable manner, such as by machining a solidpiece of material into the proper form, molding material into the properform, or welding or otherwise connecting various components manufacturedseparately.

In particular embodiments, the flexure bearing 200 is designed with thefollowing details in mind. Maximum axial displacement of the inner hub204 could be about ±0.3 inches (about ±7.62 mm) to about ±0.4 inches(about ±10.16 mm) as measured from the neutral position of the inner hub204. Also, maximum stress placed on any portion of the flexure bearing200 could be under a specified threshold, such as 62 kilopounds persquare inch (ksi). This can be done to help ensure an adequateoperational lifetime for the flexure bearing 200. Note, however, thatthese values are examples only and that other values could be used.

FIGS. 4 through 6 illustrate other example non-rotating flexure bearings400-600 according to this disclosure. Each of these flexure bearings400-600 could be used in any suitable system. For example, each of theseflexure bearings 400-600 could represent the flexure bearings containedwithin the stacks 116 a-116 b in the system 100 of FIG. 1.

As shown in FIG. 4, the flexure bearing 400 includes an outer hub 402,an inner hub 404, and openings 406. The flexure bearing 400 alsoincludes three sets 408 a-408 c of flexure arms 410 a-410 b. In theexample shown in FIG. 4, there are three sets 408 a-408 c of flexurearms positioned radially around a central axis at a spacing of about120°. As with the flexure bearing 200, the flexure arms 410 a-410 b helpto hold a cryocooler component or other device at a desired locationwhile reducing or minimizing rotation of the device.

The flexure bearing 400 shown in FIG. 4 is similar in structure to theflexure bearing 200 of FIG. 2. However, the flexure arms 410 a-410 b inFIG. 4 do not follow as curved a path as the flexure arms 210 a-210 b inFIG. 2, making the flexure arms 410 a-410 b somewhat shorter. This couldmake the cryocooler component or other device less susceptible todisplacement but can increase the stresses placed on the flexure arms410 a-410 b (since the stresses are distributed along shorter paths).

As shown in FIG. 5, the flexure bearing 500 includes an outer hub 502,an inner hub 504, and openings 506. The flexure bearing 500 alsoincludes three sets 508 a-508 c of flexure arms 510 a-510 b. In theexample shown in FIG. 5, there are three sets 508 a-508 c of flexurearms positioned radially around a central axis at a spacing of about120°. As with the flexure bearings 200 and 400, the flexure arms 510a-510 b help to hold a cryocooler component or other device at a desiredlocation while reducing or minimizing rotation of the device.

In FIG. 5, the path followed by each flexure arm 510 a-510 b is shorterstill, where much of each flexure arm 510 a-510 b moves tangentiallyaround a central axis of the flexure bearing 500. The non-tangentialportions of each flexure arm 510 a-510 b include the flexure arm's “loopback” region 512 and the portions connecting that flexure arm to thehubs 502-504.

As shown in FIG. 6, the flexure bearing 600 includes an outer hub 602,an inner hub 604, and openings 606. The flexure bearing 600 alsoincludes three sets 608 a-608 c of flexure arms 610 a-610 b. In theexample shown in FIG. 6, there are three sets 608 a-608 c of flexurearms positioned radially around a central axis at a spacing of about120°. As with the prior flexure bearings, the flexure arms 610 a-610 bhelp to hold a cryocooler component or other device at a desiredlocation while reducing or minimizing rotation of the device.

The flexure arms 610 a-610 b are similar to the flexure arms 510 a-510 bin FIG. 5, except a number of circular openings 614 and semi-circularopenings 616 are present in the flexure arms 610 a-610 b. These openings614 can alter various characteristics of the flexure bearing 600, suchas its axial stiffness and natural frequency.

In all of the flexure bearings 400-600 shown in FIGS. 4 through 6, theflexure arms in each set of flexure arms are mirror images of oneanother and therefore symmetric. This helps to reduce or minimizerotation of each flexure bearing's inner or outer hub (depending onwhich is secured to a support structure) since displacement of oneflexure arm is substantially counteracted by the displacement of themirror-image flexure arm.

Although FIGS. 2 through 6 illustrate examples of non-rotating flexurebearings, various changes may be made to FIGS. 2 through 6. For example,the number of flexure arms is for illustration only and can change asneeded. As a particular example, depending on the size of a flexurebearing, the flexure bearing could include more than three sets offlexure arms. Also, the flexure arms need not be curved and could beformed from substantially straight sections.

FIG. 7 illustrates an example method 700 for using a non-rotatingflexure bearing according to this disclosure. For ease of explanation,the method 700 is described with respect to the flexure bearing 200being used in the system 100 of FIG. 1. However, the method 700 couldinvolve the use of any other flexure bearings (such as the flexurebearings 400-600) in any other suitable system.

As shown in FIG. 7, at least one flexure bearing is coupled to a supportstructure and to a device needing positioning at step 702. This couldinclude, for example, inserting bolts or other connectors throughopenings 206 of the flexure bearing 200. This can be done to secure theflexure bearing 200 to a compressor 102 or other cryocooler component ordevice and to a housing 112.

The device coupled to the flexure bearing is displaced at step 704. Thiscould include, for example, external forces causing the compressor 102to be displaced axially along the central axis of the flexure bearing200. As a result, symmetric flexure arms in the flexure bearing aredeformed at step 706. This could include, for example, rotation of a hub202-204 caused by deforming one flexure arm being substantiallycancelled by the rotation of the hub 202-204 caused by deforming themirror-image flexure arm. This helps to reduce or minimize rotation ofthe device during the displacement at step 708. The device returnssubstantially to its desired resting location at step 710. This couldinclude, for example, the flexure bearing 200 causing the compressor 102to return to a neutral position once the external force that caused thedisplacement is removed.

Although FIG. 7 illustrates one example of a method 700 for using anon-rotating flexure bearing, various changes may be made to FIG. 7. Forexample, while shown as a series of steps, various steps in each figurecould overlap, occur in parallel, occur in a different order, or occurmultiple times.

It may be advantageous to set forth definitions of certain words andphrases used throughout this patent document. The terms “include” and“comprise,” as well as derivatives thereof, mean inclusion withoutlimitation. The term “or” is inclusive, meaning and/or. The phrase“associated with,” as well as derivatives thereof, may mean to include,be included within, interconnect with, contain, be contained within,connect to or with, couple to or with, be communicable with, cooperatewith, interleave, juxtapose, be proximate to, be bound to or with, have,have a property of, have a relationship to or with, or the like.

While this disclosure has described certain embodiments and generallyassociated methods, alterations and permutations of these embodimentsand methods will be apparent to those skilled in the art. Accordingly,the above description of example embodiments does not define orconstrain this disclosure. Other changes, substitutions, and alterationsare also possible without departing from the spirit and scope of thisdisclosure, as defined by the following claims.

What is claimed is:
 1. An apparatus comprising: an outer hub and aninner hub, the hubs configured to be secured to a support structure andto a device; and multiple sets of flexure arms connecting the outer huband the inner hub, each set of flexure arms including symmetric flexurearms; wherein each flexure arm comprises one or more circular openings.2. The apparatus of claim 1, wherein the sets of flexure arms arepositioned radially around a central axis of the apparatus.
 3. Theapparatus of claim 2, wherein the apparatus includes three sets offlexure arms having a spacing of about 120° around the central axis ofthe apparatus.
 4. The apparatus of claim 1, wherein each flexure armfollows a substantially curved path between the outer hub and the innerhub.
 5. The apparatus of claim 1, wherein the symmetric flexure arms ineach set are configured such that twisting of one flexure arm in one setis substantially counteracted by twisting of another flexure arm in thatset.
 6. The apparatus of claim 1, wherein each flexure arm follows apath that includes one or more “S” curves and a loop back region inwhich the flexure arm substantially reverses a direction of travelwithin the apparatus.
 7. The apparatus of claim 1, wherein a portion ofeach flexure arm follows a tangential path around a central axis of theapparatus.
 8. The apparatus of claim 7, wherein each flexure arm furthercomprises one or more semi-circular openings.
 9. A system comprising: adevice; a support structure; and a flexure bearing configured to connectthe device to the support structure, the flexure bearing comprising: anouter hub and an inner hub, the hubs configured to be secured to thesupport structure and to the device; and multiple sets of flexure armsconnecting the outer hub and the inner hub, each set of flexure armsincluding symmetric flexure arms; wherein each flexure arm comprises oneor more circular openings.
 10. The system of claim 9, wherein theflexure bearing includes three sets of flexure arms positioned radiallyaround a central axis of the flexure bearing and having a spacing ofabout 120°.
 11. The system of claim 9, wherein each flexure arm followsa substantially curved path between the outer hub and the inner hub. 12.The system of claim 9, wherein the symmetric flexure arms in each setare configured such that twisting of one flexure arm in one set issubstantially counteracted by twisting of another flexure arm in thatset.
 13. The system of claim 9, wherein each flexure arm follows a paththat includes one or more “S” curves and a loop back region in which theflexure arm substantially reverses a direction of travel within theflexure bearing.
 14. The system of claim 9, wherein a portion of eachflexure arm follows a tangential path around a central axis of theflexure bearing.
 15. The system of claim 14, wherein each flexure armfurther comprises one or more circular or semi-circular openings. 16.The system of claim 9, wherein: the device comprises a movable componentof a cryocooler; and the support structure comprises a housing of thecryocooler.
 17. A method comprising: displacing a device coupled to aflexure bearing, the flexure bearing comprising an outer hub and aninner hub, the hubs configured to be secured to the device and to asupport structure; deforming flexure arms in the flexure bearing as aresult of the displacement, the flexure bearing comprising multiple setsof flexure arms connecting the outer hub and the inner hub, each set offlexure arms including symmetric flexure arms and one or more circularopenings; and substantially preventing rotation of the device during thedisplacement.
 18. The method of claim 17, wherein the symmetric flexurearms in each set are configured such that twisting of one flexure arm inone set is substantially counteracted by twisting of another flexure armin that set.
 19. The method of claim 17, wherein the flexure bearingincludes three sets of flexure arms positioned radially around a centralaxis of the flexure bearing and having a spacing of about 120°.
 20. Themethod of claim 17, wherein each flexure arm follows a substantiallycurved path between the outer hub and the inner hub.